Arc-describing instrument



F. H. MunRAw ARC DESCRIBING INSTRUMENT.

f APPLIQATION FILED JULY-3,1920. -;1,427,493.

Patented Aug. 29, 1922.

2 SHEETSSHEET I.

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Specification of Letters silent. Patented Aug. 29, 1922.

Application filed. Julyt, 1920. Serial No. 393,891.

T 0 all whom it may concern:

Be it known that I, remain MURRAY. citizen of the United States ofri'merica, and resident of Cambridge in the county of Middlesex and State of Massachusetts, hare invented new and useful Improvements in Arc-Describing instruments. of which the following is a specification.

My invention relates to instruments for describing ares and is particularly adapted for draftsmans use. 'fhe object of the invention is to provide a draftmans instrument which although compact in' its proportions is capable of drawing with accuracy arcs of circles of any radius greater than that within the range of ordinary compasses up to infinity. In the drawings hereto annexed which illustrate instruments which exemplify myinvention,

Fig. 1 is aview in perspective of one form of are describing instrument;

Fig. 2 is a diagram illustrating the principle of operation of the instrument shown in Fig. 1-; I i

Fig. 8 is a View in perspective of "another form of instrument; and

Fig. 4 is a diagram illustrating the principle of operation of the instrument shown in Fig. 3.

Referring first to Fig. 1. A represents a frame which will preferably be made of metal and in this frame slideways D are formed in which the legs L. L are slidably and adjustably mounted. The legs are properly confined in their slide-ways by means of metallic covers B in which are mounted set screws C which bearing on the legs L, L in the slide-ways D serve to fix the said legs at any desired degree of extension from the frame A. The outer and lower ends of the legs L, L are suitably pointed. An arm R is mounted in the frame A. pivotally with respect to said frame and therefore with relation to the legs L, L. The pivotal mounting of the arm R is by means of shaft S to which the arm R is attached, adapted to carry a line drawing instrument such as I. This il' trument will preferably be rotatably adjustable on the arm R as by means of the offset bracket F which is provided with a clamp as at F with which it may be set at any desired angle about the axis of the arm B. This rotatable adjustment will enable the drawing instrument I to be set in proper relation to the paper on which an arc is to be described.

if the extension of the legs L, L from the frame .ei. be such that the axis of the shaft S is pa allel r" in through the pen .sof the h ii H' I re frame A be then rocked on at linens an ai-zis. it is obvious that the line drawing instrument I if allowed to rest upon the yer and to move over it will describe a night line. Tf however; the instrument be adjusted that the axis of the shaft S .hich is the pivotal a xisyof the arm It stands at an angle greater than Zero with a th strai' ht line passstrai ht line passing through the points L.

L", a rocking moren'ient of the frame a will cause the line drawing instrument I to more in the arc of a circle. Referring to Fig.- 2: The legs of the instrument may be 'so ad usJted that the leg L extends further from the frame than the leg L and the frame therefore resting on the points of these "legs is tilted and a line drawn in prolongation of the axis of the shaft S will intersect the straight line passing through the points of the legs L. L at the point '9; this point is the center of the circle, will be the 'disz'zance V between the instrument T and the center 0. This radius V may be -waiied in length from the minimum prescribed by the proportions of the "instrument itself and infinity. j

Referring now to Fig. 3 the frame a of the instrun'lent is generally-cireular inform and is provided with lugs (1 a in which the lens Z, Z are fixed; these legs extending equally'irom the frame. The frame isnot completely circularbut is segmental so that the arm r may swing from one side of the frame to the other through the gap in the frame. This arm is pivotally mounted by being secured to a shaft 8, which is journaled in the segmental slide 7t. The slide it lies in an annular channel formed on the inside of I the frame 64., one side of said channel being provided by the segmental cover plate a secured by means of set screws (1? to the frame a so that it performs the function of a clamp to hold the segmental slide it in any desired position. The line drawing instrument 2' is mounted and rotatably adjustable on the arm By slackening the set screws 0. the segmental. slide it may hemade to assume any desired angle (within the structural limits of the instrument) with a straight line passing throughthe pointed ends of the legs Z Z, and thus as in the case of the instrument shown in Fig. 1 the line er as the a K ns circle may be varied from prescribed by the structural. the instrument to infinity.

Referring to Fig. 4: the shaft 8 is shown adjusted at such an angle to the line passing through the ends of the Z, Z that geometrical prolongation of the axis of the shaft intersects the said straight line at the point 0 this point is the center of the circle of which the instrument 2' will describe an are as the frame a is rocked or turned about the line passing through the points of the legs as an a The radius of that is indicated by Q).

I claim i. In an arc-describing instrument, a frame adapted for angl'ilar movement about an axis, an arm, adapted to carry a linedrawing instrument, mounted in pivotal relation to the frame, the said arm and frame being relatively adjustable to vary the angle between the pivotal axis of the arm and the axis of angular movement of. the frame.

2. In an arc-describing instrument, the combination of supporting means including a pair of legs, an arm, adapted to carry a line-drawing instrument, mounted in pivotal relation to the supporting means, the said arm and legs being adjustable relatively to each other to vary the angle between the pivotal axis of the arm and the straight line passing through the ends of the legs.

3. In an arc-describing instrumei'it. the combination of a frame, a pair of le. tached to the frame, a shaft pivotally m ed in the fra1ne,an arm on the shaft ads pted to carry a line-drawing instrument. thev legs and shaft being adjustable relatively to each limita tions of other to vary the angle between the axis of the shaft and the straight line passing through the ends of the legs.

l. In an arc-describing instrument, the combination of a frame, a pair of legs mot ed in the frame, a shaft pivoted in the irame, an. arm on the shaft adapted to carry a line-drawing instrument, the said legs being adjustable to vary their relative extension from the frame.

5. In an arc-describing instrument, the combination of a frame, a pair of legs slidabl and adjustably mounted in the frame, a shaft pivoted in the frame, and an arm on the shaft adapted to carry a line drawing instrument.

6. In an arc-describing instrument, the combination of a pair of legs. an arm mounted in pivotal relation to the legs, a linedrawing instrument mounted and rotatably adjustable on said arm, the said arm and legs being relatively adjustable to vary the angle between the pivotal axis of the arm and the straigl'it line passing through the ends of the legs.

7. In an arc-describing instrument, the con'ibination of a frame including a pair of legs, a shaft pivoted in the frame, an arm on the shaft, a line-drawing instrun'ient mounted and rotatably adjustable on the arn, the shaftand frame being adjustable relatively to each other to vary the angle between the axis of the shaft and the straight line passing); through the ends of the legs.

8. In an arc-describing instrument, the combination of a frame, a pair of legs mounted in the frame, a shaft pivoted in the frame,

an arm on the shaft, a line-drawing instru ment mounted and relatively adjustable on.

the arm. the said legs being adjustable to arj" their relative extension from the frame.

In an arc-describing instrument, the :ombination of a frame, a pair of legs slidably and adjustably mounted in the frame,

a shaft pivoted in the frame, an arm on the shaft, and a line-drawing instrmnent mounted and rotatably adjustable on said arm.

Signed by me at Boston, Massachusetts, this first (lay of July, 1920.

FORREST H. ll IURRAY. 

